1. Field of the Invention
The present invention relates to a method for producing silicone rubber powder. More particularly, this invention relates to a method for producing silicone rubber in the form of a powder that is suitable for use as an electrical insulating material and is prepared from a heat-curable liquid organosiloxane composition.
2. Description of the Prior Art
Methods known in the art for producing silicone rubber powder include pulverizing cured silicone rubber into a powder after it has been frozen with dry ice, and pulverizing cured silicone rubber into a powder using a grinder at ambient temperature. The primary disadvantage of these methods is the difficulty of obtaining microfine particles of uniform shape at a high production rate.
Copending U.S. patent application Ser. No. 034,368, filed on Apr. 6, 1987 in the names of two of the present three inventors teaches a method for forming a powdered form of silicone rubber. In accordance with this method a liquid heat curable silicone rubber composition is emulsified in water in the presence of a surfactant at a temperature of from 0.degree. to 25.degree. C. The emulsion is then sprayed into a water bath maintained at a temperature of at least 25.degree. C. and sufficiently high to cure the ingredients of the silicone rubber composition. The disadvantage of this method is that the specific resistivity of the resultant particles is in the order of from 10.sup.12 to 10.sup.13 ohm-centimeter, which is typically too low for an electrical insulating material.
The present inventors endeavored to find a method for preparing a powder form of silicone which would not suffer from the aforementioned problems. The present invention was developed as a result of these investigations.